In recent years there has been an increase in research on the use of hyperthermia in radiation therapy. There are reports in which high temperatures have induced cell and tumor susceptibility to radiation. The research proposed here is to investigate the genetic mechanism of how hyperthermia increases cell death due to radiation. Radiation induced genetic damage to Drosophila has been extensively studied and there are excellent methods available to quantitatively determine the extent. It is proposed to investigate what hyperthermia before and after radiation does to induce genetic damage as measured by chromosome loss, nondisjunction, induction of dominant and recessive lethals and translocations. Evidently a repair system or systems are impaired by the hyperthermia upon radiation induced damage will be studied. Radiation sensitive strains of Drosophila which are deficient in four different repair processes of DNA will be employed to determine the effects of hyperthermia upon radiation induced genetic damage.